Chapter Questions
What are the three principal classes of animal food?
Life is dependent on four major classes of biomolecules. What are they?
Of the sugars listed in Table $20.1$, which is the sweetest disaccharide? Which is the sweetest monosaccharide? (Invert sugar is a mixture of glucose and fructose, so it should not be considered.)
Indicate the three types of carbohydrates. Which is the simplest?
What is an aldose, an aldotetrose, a ketose, a ketohexose? Give an example of each.
Classify the following as a monosaccharide, disaccharide, or polysaccharide: glucose, sucrose, maltose, fructose, cellulose, lactose, glycogen, galactose, starch, and ribose.
Draw structural formulas in the open-chain form for ribose, glucose, fructose, and galactose.
Draw structural formulas in the cyclic form for ribose, glucose, fructose, and galactose.
State the properties and the sources of ribose, glucose, fructose, and galactose.
The molecular formula for lactic acid is $\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{3}$, and its structural formula is $\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{COOH}$. Is this compound a carbohydrate? Explain.
What is the monosaccharide composition of(a) sucrose(b) maltose(c) lactose(d) starch(e) cellulose(f) glycogen
Draw structural formulas in the cyclic form for sucrose and maltose.
If the most common monosaccharides have the formula $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}$, why do the resulting disaccharides have the formula $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}$, rather than $\mathrm{C}_{12} \mathrm{H}_{24} \mathrm{O}_{12}$ ?
Write equations, using structural formulas in the cyclic form, for the hydrolysis of(a) sucrose(b) maltoseWhat enzymes catalyze these reactions?
Discuss the similarities and differences between starch and cellulose.
In what form is carbohydrate stored in the body?
Discuss, in simple terms, the metabolism of carbohydrates in the human body.
State the natural sources of sucrose, maltose, lactose, and starch.
Invert sugar, obtained by the hydrolysis of sucrose to an equalmolar mixture of fructose and glucose, is commonly used as a sweetener in commercial food preparations. Why is invert sugar sweeter than the original sucrose?
Use molecular structure to explain the following:(a) Fructose is a ketone.(b) Glucose is an aldehyde.
What is the empirical formula for monosaccharides?
What change in oxidation state is experienced by the carbon in the combustion of sugar, $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}$, to $\mathrm{CO}_{2}$ ?
The molar mass of cellulose is approximately $6.0 \times 10^{5} \mathrm{~g} / \mathrm{mol}$, and the molar mass of a soluble starch is on the order of $4.0 \times 10^{3} \mathrm{~g} / \mathrm{mol}$. The monomer unit in both of these molecules has the empirical formula $\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{5}$. The units are about $5.0 \times 10^{-10} \mathrm{~m}$ long. About how many units occur in each molecule, and how long are the molecules of cellulose and starch as a result?
What are the differences between saturated fats and unsaturated fats?
Are the fatty acids in vegetable oils more saturated or unsaturated than those in animal fats? Explain your answer. (Table 20.2)
What properties of molecules cause them to be classified as lipids?
Write structural formulas for glycerol, stearic acid, palmitic acid, oleic acid, and linoleic acid.
Distinguish both chemically and physically between a fat and a vegetable oil.
What is a triacylglycerol? Give an example.
Write the structure for tristearin, a fat in which all the fatty acid units are stearic acid.
Write the structure of a triacylglycerol that contains one unit each of linoleic, stearic, and oleic acids. How many other formulas are possible in which the triacylglycerol contains one unit each of these acids?
Write equations for the saponification of(a) tripalmitin (a fat in which all the fatty acids are palmitic acid)(b) the triacylglycerol of Question 31 .Which product(s) are soaps?
How can vegetable oils be solidified? What is the advantage of solidifying these oils?
What functions do fats have in the human body?
Which fatty acids are essential to human diets?
Draw the structural formula of cholesterol.
Draw the ring structure that is common to all steroids.
Write the formula for the triacylglycerol formed from(a) glycerol and butanoic acid(b) glycerol and one molecule each of stearic $\left(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COOH}\right)$, palmitic $\left(\mathrm{C}_{15} \mathrm{H}_{31} \mathrm{COOH}\right)$, and myristic $\left(\mathrm{C}_{13} \mathrm{H}_{27} \mathrm{COOH}\right)$ acids
In a linear peptide, what are the N-terminal residue and the C-terminal residue?
Which of the common amino acids have more than one carboxyl group? Which have more than one amino group? (Table 20.3) insulin? (Figure 20.3)
How many disulfide linkages are there in each molecule of beef insulin? (Figure 20.3)
List six foods that are major sources of proteins.
What functional groups are present in amino acids?
Why are the amino acids of proteins called $\alpha$-amino acids?
In Table 20.3, which amino acids (a) are aromatic, (b) contain sulfur, (c) contain an - $\mathrm{OH}$ group?
Write the full structure for the two possible dipeptides containing glycine and phenylalanine.
Write structures for(a) glycylglycine(b) glycylglycylalanine(c) leucylmethionylglycylserine
Using amino acid abbreviations, write all the possible tripeptides containing one unit each of glycine, phenylalanine, and leucine.
The artificial sweetener aspartame is a dipeptide made from two amino acids, aspartic acid and phenylalanine. Write two possible structures for this dipeptide.
What are essential amino acids? Write the names of the amino acids that are essential for humans.
When proteins are eaten by a human, what are the metabolic fates of the protein material?
Why should protein be continually included in a balanced diet?
In the polypeptide Tyr-Gly-His-Phe-Val, identify the N-terminal and the C-terminal residues.
How are polypeptides numbered? Number the polypeptide in Question $53 .$
What is the name of the bond that bonds one $\alpha$-amino acid to another in a protein?
How can you discern the difference between an amino acid and an ordinary carboxylic acid?
What are enzymes, and what is their role in the body?
What is meant by specificity of an enzyme?
Differentiate between the lock-and-key and induced-fit models for enzyme function.
What is meant by enzyme specificity?
What is the function of enzymes in the body?
What are the components of chromosomes?
In the four nucleotide units of DNA shown in Figure 20.6, which of these components are part of the backbone chain and which are off to the side: the nitrogen bases, the deoxyribose, and the phosphoric acid?
In the double-stranded helix structure of DNA, which bases are always hydrogen-bonded to the following: cytosine, thymine, adenine, and guanine? (Figure 20.7)
Write structural formulas for the compounds that make up DNA.
(a) What are the three units that make up a DNA nucleotide?(b) List the components of the four types of nucleotides found in DNA.(c) Write the structure and name of one of these nucleotides.
Briefly describe the structure of DNA as proposed by Watson and Crick.
What is the role of hydrogen bonding in the structure of DNA?
Explain the concept of complementary bases and how it relates to DNA.
A segment of a DNA strand has a base sequence of C-G-A-TT-G-C-A. What is the base sequence of the other complementary strand of the double helix?
Explain the replication process of DNA.
Briefly discuss the relationship of DNA to genetics.
What are the three differences between DNA and RNA in terms of structure?
Distinguish between cell division in mitosis and in meiosis.
Specifically, where does protein synthesis occur?
What is the relationship between proteins and amino acids?
In Figure 20.7, what do the red dotted lines represent?
What is galactosemia, and how does it affect humans?
(a) Indicate which two amino acids could form an ester bond using their $R$ group side chains.(b) Draw the product of cholesterol reacting with bromine.
(a) Carboxypeptidase $\mathrm{A}$ is a digestive enzyme. A zinc ion is necessary for enzyme activity. What is the zinc ion called?(b) Some RNA strands also show enzymatic activity, but DNA does not. What are two structural differences between RNA and DNA?